Ocean Stress Project

确定洋壳内应力的方向和大小，以约束驱动板块的力的模型，是海洋钻探计划下一个十年的主要目标。虽然用超声波电视井眼扫描观测到的应力引起的井壁崩塌已经提供了这些ODP型钻孔中最大和最小主水平应力的方向，但没有对应力大小进行直接测量或估计。最近应用于陆地现场的理论发展可以扩展到在洋壳中钻出的孔，以允许根据有无崩落和其他井筒破坏现象以及地壳摩擦强度施加的约束来限制地应力的大小。该项目将通过重新分析现有的钻孔电视数据来估计地应力的大小。当井壁的周向应力集中与径向应力之差超过岩石的强度时，就会形成崩落。如果发生崩落并且岩石的强度已知，则可以对应力大小施加约束。将对热效应和孔压效应进行修正。将从观察到拉伸裂缝或崩落的深度对岩石的抗拉强度和无侧限抗压强度进行实验室测量。

Determination of the direction and magnitude of stresses within the oceanic crust to constrain models for the forces driving the plates is a principal objective of the next ten years of the Ocean Drilling Program. Although observations of stress-induced wellbore breakouts with ultrasonic televiewer wellbore scanning have provided indications of the directions of the maximum and minimum principal horizontal stresses in these ODP boreholes, no direct measurements or estimates of stress magnitudes have been made. Recent theoretical developments applied to sites on land can be extended to holes drilled in the oceanic crust to allow constraints to be placed on the magnitudes of in situ stresses based on the presence or absence of breakouts and other wellbore failure phenomena, and from constraints imposed by the frictional strength of the crust. This project will estimate magnitudes of in situ stress by re- analyzing existing borehole televiewer data. Breakouts will form when the difference between the circumferential stress concentration and the radial stress at the borehole wall exceeds the strength the rock. Constraints can be placed on the stress magnitudes if breakouts occur and if the strength of the rock is known. Corrections will be made for thermal effects and pore pressure effects. Laboratory measurements will be made of the tensile and unconfined compressive strength for rock from the depth at which observations of tensile cracks or breakouts are obtained.